With the introduction of the microwave oven, a huge demand has been created for disposable food and beverage containers which may be heated in conventional microwave ovens. These containers eliminate the necessity of utilizing a separate microwavable bowl and the inconvenience related thereto, and provide a container which is used for both storing food and beverage items, heating those items, and subsequently using the container as a serving bowl or tray. Following use, the microwavable bowl may be conveniently discarded or recycled rather than cleaned. As used herein, the term “foodstuffs” applies to both solid and liquid food and beverage items, including but not limited to pasteurized liquids such as milk products, soups, formula, and solids such as meats, vegetables, fruits, etc.
In general, metal containers have not been utilized for heating foodstuffs in microwave ovens due to the likelihood of electrical “arcing”, and the general public misconception that metal materials are incapable of being used in conventional microwave ovens. Although previous attempts have been made to design microwavable metal containers, these products have generally been very limited and impractical in their design and use. For example, U.S. Pat. Nos. 4,558,198 and 4,4689,458 describe microwavable metal containers which have height limitation of less than about 1 inch, and are thus not practical for storing any significant volume of foodstuffs.
U.S. Pat. No. 5,961,872 to Simon et al, (the '872 patent”) discloses a microwavable metal container which utilizes a microwavable transparent material. However, the '872 patent does not utilize a hermetic seal which is sufficient to safely store food items under a vacuum for long periods of time, and which requires that the entire lower portion and sidewall of the metal container be enclosed within an electrical insulation material to prevent arcing. Further, the device requires that the side walls of the container have a height less than about 40 percent of the wavelength of the microwave radiation used to heat the object, which is not overly practical or functional.
More recent attempts to store and cook food in microwavable containers have been accomplished by using non-metallic plastic and foam type materials. Although these products are suitable for use in microwave ovens, and are generally accepted by the consuming public, they have numerous disadvantages when compared to metallic containers. More specifically, non-metallic foam and plastic containers have very poor heat transfer characteristics, and these types of containers require significant more time to heat and cool in a food processing plant. Thus, these types of containers are very time-consuming and expensive to fill and sterilize during filling operations, and are thus inefficient for mass production.
Further, non-metallic containers are not as rigid as metal containers, and thus cannot be stacked as high as metal containers which limits the volume which can be shipped, and thus increases expenses. Additionally, non-metallic containers are not durable, and are prone to damage and leaking during shipment and placement for sales, thus adding additional expense. Furthermore, multi layer barrier plastics and foams are generally not recyclable like metal containers, which fill landfills and are thus not environmentally friendly.
Additionally, most conventional foam containers are not durable and susceptible to damage when subjected to high heat such as that found during a retort operation wherein a foodstuff in a container is sterilized with steam or other means.
Finally, foodstuffs cooked in non-metallic plastic and foam containers in a microwave oven generally overheat and burn next to the container surface, while the foodstuff in the center of the container heats last, and thus requires stirring for adequate heating. Further, there are general health concerns regarding the possible scalping of chemicals and the subsequent altered taste when cooking foods in non-metallic containers, especially since non-metallic plastics and foams can melt and deform when overheated.
Thus, there is a significant need in the food and beverage container industry to provide an economical metallic container which may be used for cooking foodstuffs in a microwave oven and which eliminate many of the health, shipping and filling problems described above.